How severe is CVE-2021-32637?

CVE-2021-32637 has a CVSS score of 10/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-32637?

CVE-2021-32637 affects the following packages: github.com/authelia/authelia/v4 (Go). Ecosystems affected: Go.

How do I fix CVE-2021-32637?

Update github.com/authelia/authelia/v4 to 4.29.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32637 is resolved across your whole dependency graph.

How do I detect CVE-2021-32637 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/authelia/authelia/v4. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2021-32637 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2021-32637?

O3 pinpoints whether CVE-2021-32637 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2021-32637 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-32637, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-32637?

CVE-2021-32637 has an EPSS (Exploit Prediction Scoring System) score of 1.9%, placing it in the 77th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2021-32637 published, and has it been updated?

CVE-2021-32637 was published on May 28, 2021 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2021-32637: v4 (Critical 10)

EPSS Exploitation Probability

via FIRST.org ↗

1.9%probability of exploitation in next 30 days

Lower Risk77th percentile+1.40%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

🐹github.com/authelia/authelia/v4

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Authelia is a a single sign-on multi-factor portal for web apps. This affects uses who are using nginx ngx_http_auth_request_module with Authelia, it allows a malicious individual who crafts a malformed HTTP request to bypass the authentication mechanism. It additionally could theoretically affect other proxy servers, but all of the ones we officially support except nginx do not allow malformed URI paths. The problem is rectified entirely in v4.29.3. As this patch is relatively straightforward we can back port this to any version upon request. Alternatively we are supplying a git patch to 4.25.1 which should be relatively straightforward to apply to any version, the git patches for specific versions can be found in the references. The most relevant workaround is upgrading. You can also add a block which fails requests that contains a malformed URI in the internal location block.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/authelia/authelia/v4`	≥ 4.0.0-alpha1&&< 4.29.3	4.29.3

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/authelia/authelia/v4. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/authelia/authelia/v4 to 4.29.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32637 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-32637 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2021-32637. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

Authelia is a a single sign-on multi-factor portal for web apps. This affects uses who are using nginx ngx_http_auth_request_module with Authelia, it allows a malicious individual who crafts a malformed HTTP request to bypass the authentication mechanism. It additionally could theoretically affect other proxy servers, but all of the ones we officially support except nginx do not allow malformed URI paths. The problem is rectified entirely in v4.29.3. As this patch is relatively straightforward we can back port this to any version upon request. Alternatively we are supplying a git patch to 4.25

O3 Security · Impact-Aware SCA

Is CVE-2021-32637 in your dependencies?

O3 detects CVE-2021-32637 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works

CVE-2021-32637